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			PubMed Journals: J Biol Chem

  Source:		PMID: 8395513


    		J Biol Chem. 1993 Sep 5;268(25):18626-32.
     
			Identification of phosphorylation sites
			in the recombinant catalytic subunit of
			cAMP-dependent protein kinase.

			Yonemoto W(1), Garrod SM, Bell SM, Taylor
			SS.

			Author Information
			(1) Department of Chemistry,
			University of California, San Diego
			La Jolla 92093-0654.

			The catalytic subunit of cAMP-dependent
			protein kinase expressed in Escherichia
			coli is a phosphoprotein. By in vivo labeling
			with [32Pi]orthophosphate, the sites of
			phosphorylation were identified as Ser-10,
			Ser-139, Thr-197, and Ser-338. Two of these
			sites, Thr-197 and Ser-338, are found in
			the mammalian enzyme (Shoji, S., Titani,
			K., Demaille, J. G., and Fischer, E. H.
			(1979) J. Biol. Chem. 254, 6211-6214). The
			predominant isoform is phosphorylated at
			Ser-10, Ser-338, and Thr-197. The isoforms
			cannot be readily interconverted by in vitro
			autophosphorylation, suggesting that the
			phosphates are relatively stable once the
			mature protein is assembled. Unlike the
			mammalian enzyme, the recombinant enzyme
			is not myristylated at its animo terminus. By
			coexpressing the catalytic subunit and N-myristyl
			transferase, the recombinant catalytic subunit
			is myristylated, and, under these conditions,
			phosphorylation at Ser-10 is reduced. The
			fact that recombinant catalytic subunit
			mutants that are enzymatically impaired
			are not phosphorylated in vivo indicates
			that the phosphorylation of the catalytic
			subunit observed in E. coli is due to
			autophosphorylation. Whether this process
			is intramolecular or intermolecular cannot
			be distinguished. Although autophosphorylation
			accounts for the modification of the catalytic
			subunit when it is expressed in E. coli,
			there may be heterologous protein kinases
			that are responsible for its in vivo phosphorylation
			when the enzyme is expressed in eukaryotic
			cells.

			PMID: 8395513 [Indexed for MEDLINE]

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